STANFORD — Derek Mason’s side of the ball is loaded. The Stanford defensive coordinator has nine returning starters from a unit that was one of the best in the nation last season, held high-powered Oregon to 14 points and powered Stanford’s run to the Pac-12 title.

And yet, Mason frets.

“What happened in 2012 has nothing to do with 2013,” Mason said Saturday. “People make the assumption that there’s a carry-over. But every year, the team is different.”

Mason is focused on three areas during spring practice. Two of them — developing depth on the defensive line and experimenting with linebacker combinations — are nice problems to have.

But the secondary is a concern, especially at cornerback.

Alex Carter has one spot locked down after a terrific freshman season, but Stanford lost its other starter, Terrence Brown, who turned pro with one year of eligibility remaining.

Wayne Lyons is a candidate to start but hasn’t been at full speed since a foot injury he suffered early in the 2011 season.

Another option, Barry Browning, will miss spring practice because of what coach David Shaw called a “minor procedure.”

The other candidates have minimal, if any, experience.

So limited are the options that nickel backs Usua Amanam and Ronnie Harris are taking reps on the outside.

“We have to figure out who our best players are and where the pieces fit,” Mason said. “We’ll move guys around all spring.”

The competition at center includes not one but two players who started at guard last season: Khalil Wilkes, the early favorite to replace Sam Schwartzstein; and Kevin Danser, who has looked good during his stints at the position.

Junior Conor McFadden is also in the mix.

For the second consecutive year, nobody will wear uniform No. 12, former quarterback Andrew Luck’s number.

Redshirt freshman tailback Barry Sanders is off limits to the media, per an edict from Shaw.

Sanders is the son and namesake of the former Heisman Trophy winner and Pro Football Hall of Fame running back.

“I’m not going to put a guy out in front because of his name,” Shaw said. “There have been a bunch of interview requests for Barry. There’s no reason he should have a media session before his first game.”